Air-swept pulverizer having internal flow area adjusting means



June 21, 1949. e. B. EBERSOLE I 2,473,514

AIR iWEPT PULVERIZER HAVING INTERNAL FLOW AREA ADJUSTING MEANS Filed Aug. 14, 1943 3 Sheets-Sheet 1 INVENTOR. Y George B Eberso/e A TTORNE Y June 21, 1949.

G. B. EBERSOLE 2,473,514 AIR-SWEPT PULVERIZER HAVING TERNAL FLOW AREA ADJUSTING ME S Filed Aug. 14, 1943 S Shegts-Sheet 2 INVENTOR. George Eberso/e BY A TTORNE Y June 21, 1949. e. B. EBERsoLE 2,473,514 AIR-SWEPT PULVERIZER HAVING INTERNAL FLOW AREA ADJUSTING MEANS Filed Aug. 14, 1943 3 Sheets-Sheet 3 INVENTOR.

BY Gear e B. Eberso/e ATTORNEY Patented June 21, 1949 AIR-SWEPT PULVERIZER HAVING INTER- NAL FLOW AREA ADJUSTING MEANS George B. Ebersole, Akron, Ohio, assignorto The, Babcock & Wilcox Company, Rockleigh, N. .L, a corporation of New Jersey Application August 14, 1943, Serial No. 498,632

13 Claims. 1

The invention herein disclosed relates to a pulverizer having relatively movable grinding elements arranged to reduce various kinds of solid materials such as coal, limestone, ores, and the like, to a fine state of pulverization, the finely divided solid products being transported through and from the pulverizer by means of a current of carrier air whereby the resulting pulverizer output is a fluent mixture comprising pulverulent material suspended in the stream of carrier air; the term air" to be construed broadly as including air perse and other suitable gaseous carrier media, whether used singly or incombination. In such a pulverizer, herein identified as an airswept pulverizer, the carrier air may be introduced under pressure at a location remote from the pulverizer outlet, or may be caused to pass through the pulverizer under an induced draft condition maintained at the pulverizer outlet.

The invention is especially directed to an airswept pulverizer having a grinding zone in a lower portion thereof generally defined by grinding elements comprising a plurality of grinding balls arranged in a circular row and cooperating with the grinding surfaces of rings above and below, the carrier air being caused to flow upwardly through said zone in opposition to the downward feed of raw unground material, and being admitted to said zone through a relatively narrow annular throat to provide a sufficiently high velocity to eiTect separation of finely ground particles from coarser particles, and to promptly remove such finely divided products from the grinding zone for continuous discharge from the pulverizer.

When such a pulverizer is operated at varying capacities, it is customary to vary the rate of air flow through the pulverizer in appropriate relation to the weight of pulverized material being discharged per unit of time; in general, a greater quantity of air being supplied for higher output capacities than for lower-capacities. When coal for example is being pulverized, for use in burners having a direct connection with the pulverizer, the rate of air flow is preferably maintained sufficiently high atvarious pulverizer outputs to provide proper burner velocities and to prevent coal from accumulating in the pulverizer faster than it is carried out by the air; on the other hand, too high a rate of air flow for a given output will sweep the pulverizer of coal too rapidly with a resulting depreciation in coal fineness.

It is evident that with a. fixed mechanical arrangement of parts within the pulverizer, resulting for example in a fixed throat area, the range of output capacityis limited at least in part by the characteristics of air flow'through the throat passage and the amount of pressure drop involved at one or the other of the extreme load conditions, For example, a pulverizer may be capable of operating efficiently at maximum load with the desired velocity of air flow through and adjacent the grinding zone, and with a normal pressure drop value, whereas at minimum rating due to the decrease in air flow,'the velocity of airflow into and through the grinding zone may become less than that desired for satisfactory separation of the fine and coarse particles, and the continuous removal of the fines from.- the grinding zone. If the internal mechanical relation of parts is fixed for a suitabl velocity of air flow through the throat andgrinding zone at minimum rating, the pressure drop through the pulverizer may become excessive at maximum rating, resulting in coarseness of theproduct and abnormal increase in fan power required to maintain the required currentof carrier air.

An object of the subject invention is therefore to provide an air-swept pulverizer having internal flow area adjusting means whereby the pulverizer may be operated at varying outputs while maintaining a minimum variation in air now characteristics through and adjacent the grinding zone.

An additional object is to provide an internal mechanical arrangement of parts Within an airswept pulverizer whereby the velocity rate of air admission to the grinding, zone can be maintained within a predetermined range irrespective of variations in the quantity of air supplied.

Another object is to providean air-swept pulverizer wherein the mechanical relation of parts within the pulverizer may be adjusted in accordance with varying pulverizer output. capacities.

Further objects include adjustment of pulverizer throat area simultaneously throughout its circumference, and alternatively, selective, localized adjustment at predetermined circumferential location-s.

These and, other objects and features of the invention will be readily understood from the description to follow, particularly when read in conjunction with the accompanying drawings,

in which:

Fig. 1 is a sectional elevation of a pulverizer embodying elements of my invention;

Fig. 2 is an enlarged fragment of Fig. 1 showing certain parts in a different position of adjustment;

Fig. 3 is a sectional plan of Fig. 1 taken along line 33;

Fig. 4 is an enlargement of the operating mechanism seen in Fig. 3;

Fig. 5 is a sectional elevation showing a modification;

Fig. 6 is a partial sectional along line 6-6;

Figs. 7 and 8 are fragmentary plan and side views illustrating modified details of construction; and

Fig. 9 is a fragmentary sectional elevation showing a further modified detail.

In detail, and referring particularly to Figs. 1 to 4, inclusive, the pulverizer shown is of a known ball mill type having a casing 10 substantially cylindrical in form in which a circular series of grinding balls l2 operates between upper and lower grinding rings l4 and I6, respectively; the lower ring l6 being held stationary and the upper ring l4 being rotated about a vertical axis by means of the drive ring 18 driven through a spider 26, yoke 22, main shaft 24 and pinion shaft 26 from a convenient source of motive power, not shown. Pressure between the grinding balls and rings is resiliently maintained through springs 26 acting between the drive ring l8 and spider arm 66, and the pressure adjusted by means of longitudinally adjustable spring bolts 32. The material to be pulverized, otherwise known as raw material, is fed to the pulverizer or mill through an inlet 36 at a level preferably above the grinding zone generally defined by the grinding balls l2 together with the cooperating grinding rings I6 and 16.

A support ring, or base plate 36, at the bottom of the mill is provided with a series of radial ports 38 at intervals throughout its circumference through which air or other gaseous medium is introduced to the grinding zone for transporting finely divided particles of the raw material from the mill after pulverization, the ground material or fines being carried upwardly within the mill casing l6 and being discharged through one or more outlets 40 in the top wall of the casing. Thus, the resulting pulverizer output is essentially a fluent mixture comprising finely divided solids suspended in the gaseous carrier medium which for the purpose of this application is termed air regardless of its specific identity.

plan of Fig. 5, taken The carrier air enters the mill through an air inlet 42 leading to an air compartment 44 adjacent the periphery of the ported support ring 36 and separated from the upper mill space 46 by the conical wall 48 extending upwardly from the rim of the support ring 36 to the cylindrical wall of the casing 16.

An extension piece 50 is secured to the spider 2!] for rotation therewith, such a piece to be referred to herein as the spider extension, and being of hollow conical formation toward its base to provide a circumferential outer rim surface 52 annularly spaced from the inner periphery of the lower grinding ring I6 to form a relatively narrow annular throat passage 54 for admission of the carrier air to the grinding zone from below. The required width of the throat passage is determined from known characteristics of the mill under consideration, and may conveniently be made the same width for variable capacity operation, in accordance with the present invention, as is normally required for efiicient operation at the maximum capacity rating.

In providing for operation of the pulverizer at widely different capacities, since it is desirable to maintain a suitable minimum air flow velocity through the pulverizer throat, for a given output capacity, and a minimum variation in pressure drop for a given range of capacities, it is proposed to employ a suitable valving means whereby the effective area of the throat passage may be adjusted between maximum and minimum limits; for maximum load the effective throat area being maximum and substantially equal to the total available throat area, whereas for minimum load, the effective throat area is adjusted to its minimum value representing a fractional part of the total available throat area.

With the throat valve in any one position of adjustment, maximum, minimum, or intermediate, it will be understood that the pulverizer may be operated satisfactorily over a limited range of output capacities, but with a shift of the valve from one position to another, the individual range values are combined to provide a considerably extended total operating range, the successive range values preferably overlapping to an extent insuring a gradual transition from one range to another. In such an arrangement, the air flow velocity through the throat may be desirably maintained at the same minimum value for the low capacity limits of successive ranges.

The valving mechanism is preferably to be arranged so that the desired adjustments of throat area may be made entirely from the exterior of the pulverizer, a feature which is particularly advantageous when temporary load changes are to be accommodated as, for example, when a unit is to be put on reduced load over the weekend and then restored to normal operating load, with little or no stoppage and without structural alterations.

In one form, as illustrated in Figs. 1-4, the valving means may comprise an annular member or throat ring 56 arranged concentrically with the pulverizer throat 54 and adjustable axially in relation thereto. As seen in cross section, the ring 56 may be of substantially uniform thickness throughout, the inner and outer surface portions adjacent the top edge 58 being substantially parallel to the throat axis, and corresponding surface portions adjacent the bottom edge 66 flaring outwardly toward the air ports 38 in the support ring 36. Fig. 1 shows the ring 56 in the fully retracted position for maximum capacity, While Fig. 2 shows the ring 56 in the fully advanced position for minimum capacity where the top edge 58 of the ring is for all practical purposes level with the bottom edge 62 of the spider extension 56, thereby blocking off a portion of the throat passage 54 and affording an effective throat area less than the maximum available throat area by an amount substantially equal to the transverse cross section of the ring in the plane of its top edge 58. The diameter of the valve ring 56 at its top edge is preferably so selected that the outer annular throat space 64 constitutes the major proportion of the effective throat area, leaving a relatively small inner annular space 66 between the ring 56 and spider extension surface 52, principally for mechanical clearance purposes. A band of metal 68 may be welded or otherwise added to the rim of the spider extension to provide ample thickness to allow for machining to a true predetermined diameter.

The annular valve ring 56 is supported by spokes '10 extending radially and downwardly from a circular support plate 12, a tubular post 14 being. mounted axially of the plate and secured thereto as by welding 16, to receive an axially movable actuating rod I8 arranged for integral assembly therewith, the'rod la havi'n'g a collar 80 toward its lower end against which the lower'end of the tubular post 14' abuts, while the upper end of the rod is threaded for a: nut 82 bywhich the valve ringas'sembly and actuating rod may be removably maintained in fixed relation. I

An inverted conically formed cup-like member 84 is secured to the pulverizer base 'plate'36 'to form a support and guide for the valve ring assembly, and to provide a housing or cover for the valve ring operating mechanism to be described, the top wall or cover plate 86 beingmade removable to permit access to such'mechanism.

The cover plate'86 of the housing 84 is'recessedas'at 88 to accommodate the enlargement on the post 14 caused by the attachingmaterial 16, to allow the support plate 12 of the valve ring assembly to reston the cover plate 86 of the housing when the valve ring 56 is in its fully retracted and lowermost position as seen in Fig. 1; in this position, the projections 99 on the spokes I9 resting against the conical outside wall 92 of the housing. The cover plate 86 also provides a sleeve portion. 94 forming a guide for the post member 14 whereby axial alignment of the valve ring 56 with'the throat 54 is maintained at all positions to which the valve ring may be adjusted.

The operating mechanism for moving the valve ring 56 includes an operating shaft 96 lying adjacent'the floor of themill and extending horizontally from outside of the mill casing I9; through one of the air ports 38, through the side wall 92 of the housing 84, to a point laterally adjacent the central axis'of the pulverizer. A tube 98 suitably secured to adjacent fixed parts of the pulverizer serves as a bearing sleeve and cover for the operating shaft 96. A crank arm lllll'formed with a clevis I02 is suitably secured to the operating shaft 96 at its inner end, where a connection through link I94 is made to a clevis I 96 formed at the lower end of the actuating rod 18. The operating shaft 96 may be rotated by means of lever I08 securedto the shaft 96 exteriorly of the casing), theangular displacement being limited by the'arcuate lever slot I In incooperation with a stud or bolt II 2' secured to a stationary part of the mill structure, the bolt II2 also serving as a clamping means for holding the shaft 96 and thereby the throat ring 56 in the desired adjusted position.

In the arrangement shown, angular movement of the shaft 96 is-limited to approximately 55 which is sufiicient to rotate the crank arm I09 from a positionwhere the pin connection I I4 is :in ahorizontal plane with the axis of the shaft 96 to a position where the pin connection H4 is ina' vertical plane with the central axis of the adjustable throat ring 56. Clockwise rotation of the lever I08 through the angle 55 as described will thus cause the throat ring 56 to be moved upwardly from its lowermost maximum capacity position to its uppermost minimum capacity position, in either of which positions, orin any intermediate position, the throat ring-may be secured against accidental displacement by means of the clamping bolt II2.

In the modification according to Figs" 5 and 6, an air-swept pulverizer of the same general type as in Figs. 1 and 2 is shown, wherein a series of grinding bal1s-I2 operates between a rotatable upper grinding ring I4 and astationary lower 'gri-nding ring I6, and carrier air from i movement being of adjacent segments are the compartment 44 is directed radially through air er-tees in the base plate or support ring-36a and up'wardly through the annular throat passage 54 formed between the inner periphery of the stationary lower grinding ring I6 and the rotatable'spider extension 59a. In this form, adjustment of effective throat area is accomplished by means of a ring I positioned below the pulverizer throat 54 adjacent the bottom surface I22 of the lower grinding ring I6, thering I20 being formed as a segmental structure so that its diameter may be varied between predetermined limits to effect a correspondin variation in the effective throat area.

The ring I29 as shown is formed of arcuate segments I24 shaped as at I26 on the side facing the throat to approximate the contour of the opposing outer wall surface I 28 of the spider extension 50a whose bottom edge I3!) is positioned opposite the air ports 38 at a level slightly below the segmental ring I29. The ring segments I24 are individually movable radially "of the throat passage 54 and are resiliently held in contact with the grinding ring surface I22v by means of spring clips I32 circumferentially spaced and suitably secured to the base plate 36a as-by bolts I34, each segment being symmetrically mounted on an actuating rod I35 extending radially through a bore I33 in the solidmetal of the base plate 36a intermediate the airports 38. Each rod I36 terminates exteriorly ofthe casing III in a threaded end I49 to receive an'adjusting nut I42 whereby the desired radial posi' tion of a segment I24 may be maintained; the segment tending to be moved inwardly due to the biasing effect of the spring I44 actingin compression between spring seat I46 fixed ,to the rod'l36 and spring seat bushing I48 fixed to the mill casing I9, and the tendency for suchinward M2 opposed by the adjusting nut The ring segments I24 as shown are of substantially equal arcuate lengths and at their ends. I59 are formed parallel to their respective axes of radial movement, the arcuate lengths of individual segments'being such that when the ring I29 is contracted and all segments are moved to their normal innermost position, as indicated by the dot-and-dash circumference 52 in Fig. 6, the inner surfaces I25 collectively provide a substantially continuous surface of revolution. When the ring is expanded and all segments are moved to their extreme outermost position, as indicated by the full line showing in Fig. 6, the ends I50 separated by a small tapering gap I54 constituting a. relatively minor proportion of the total effective throat area and since such gaps are distributed about the entire circumference their presence is no detriment to successful operation.

Since the ring segments I24 are individually movable, the arrangement of Figs. 5 and 6 also enables localized adjustments or throat area to be made at predetermined circumferential locations, thereby compensating for the unequal distribution of air flow that might occur because of the single air inlet 42 at the side of the casing requiring the air to travel different distances to enter different ports 36. It is possible that irregularities in the throat surfaces or in their spaced relation, incident to machining or assembling, might also make such localized adjustment desirable.

' The arrangement of Figs. 5 and 6 may also be '75 found advantageous in that for all positions" of the ring I20, the effective throat area lies between a rotating and a non-rotating wall, thereby lessening the tendency for particles of unpulverized material to become lodged in the throat gap and possibly interfere with the intended air distribution. This is in contrast with the arrangement of Figs. 1-4 where with the ring 56 in an elevated position for minimum effective throat area, the resulting throat gap lies between opposing nonrotating walls.

Figs. 7 and 8 illustrate a modification providing for simultaneous actuation of the ring segments I24 which in these views are shown in an intermediate position of adjustment. In this form, each actuating rod IBM is suitably supthe bore I38, and at its outer end by the casing I0, and at an intermediate location carries a downwardly extending pin I56 adapted to engage a cam slot I58 in the horizontally disposed and angularly adjustable cam ring I60. The cam slots I58 are arranged at a suitable inclination to the axes of the respective actuating rods I361; so that for a predetermined angular adjustment of the cam ring I60 all segments I24 are simultaneously moved radially to the extent desired, thereby effecting substantially uniform adjustment of throat flow area throughout the entire circumference. The cam ring may be supported on bosses I62 at circumferentially spaced locations to minimize friction and to provide a clearance space between the cam ring and the mill floor so that the follower pins I56 may extend through the cam slots I58 for the full ring thickness, and furthermore so that any accumulation of dust at the bottom of the mill will not interfere with cooperation of the pins and ring. A bar or stud I64 is suitably secured to the cam ring I60 at its outer periphery, as by threads I66, and extends outwardly through an elongated slot I68 in the mill casing I thereby enabling the position of the cam ring to be adjusted from the exterior, the washer I10 and nut I12 enabling the cam ring to be clamped in the desired position of adjustment within limits ported and guided in determined either by the length of cam slot I58 or casing slot I68.

Fig. 9 illustrates a modified adjustment detail providing for positive actuation of individual rods I36 in opposite directions, and adapted for use in place of the spring arrangement shown in Fig. 5. A flanged bushing I14 rotatably mounted on the mill casing I0 is fitted with a nut I16, for example, secured thereto as by a weld I18 to prevent longitudinal displacement. The bushing is interiorly threaded for cooperation with the threaded end I40 of the actuating rod I36, whereby upon angular adjustment of the bushing by means of the nut I16 or other suitable form of adjusting means, the actuating rod I36 is longitudinally advanced or retracted to effect a corresponding radial adjustment of the associated ring segment I24. A pin I80 through the rod I36 may be employed as a stop to limit inward movement of a segment I24 to prevent inadvertent engagement of any segment with the rotatable spider extension 50a, such a stop means being adapted for similar application to the rod-adjusting detail of Fig. 5.

The invention as herein disclosed in accordance with the provisions of the statutes will be understood by persons skilled in the art to be applicable in arrangements other than those specifically described, and to include features which may be used to advantage without a correspond-' ing use of other features, within the scope of the appended claims.

I claim:

1. In a pulverizer comprising a casing having an outlet in its upper portion for pulverized material suspended in carrier air, upper and lower grinding rings in a lower portion of the space enclosed by said casing, a circular series of grinding balls intermediate said rings and cooperating therewith to define a pulverizing zone, means axially and radially fixed in relation to said lower ring and forming therewith an annular throat of constant available flow area adjacent the inner circumference of said lower ring for upward fiow of carrier air into said zone, adjustable valving means independent of and movable relative to said means forming said throat for rendering effective different proportions of said available throat area, and means for moving said adjustable means to a position rendering effective the total available flow area of said throat.

2. In a pulverizer comprising a casing having an outlet in its upper portion for pulverized material suspended in carrier air, upper and lower grinding rings coaxially arranged in a lower portion of the space enclosed by said casing, a circular series of grinding balls intermediate said rings and cooperating therewith to define a pulverizing zone, means for rotating one of said rings and thereby causing said balls to roll relative to both of said rings, means for feeding raw material to said 'zone adjacent the outer periphery thereof, means rotatable about the axis of said rings and axially fixed in relation to the lower of said rings for defining an annular throat of constant available flow area adjacent the inner circumference of said lower ring for upward flow of carrier air into said pulverizing zone, adjustable valving means independent of and movable relative to said means defining said throat for rendering effective different proportions of said available throat area, and means operable from the exterior of said casing for moving said adjustable means to a position clear of said threat for rendering effective said constant available flow area of said throat.

3. In a pulverizer comprising a casing having an outlet in its upper portion for pulverized material suspended in a current of carrier air, vertically spaced grinding rings in a lower portion of said casing including a rotatable upper ring and a non-rotatable lower ring, a circular row of grinding balls positioned intermediate said rings and cooperating therewith to define a grinding zone of said pulverizer, driving means in an upper portion of said casing for rotating said upper grinding ring and thereby causing said balls to roll relative to both of said rings, said driving means having a downwardly directed extension providing an outer surface of revolution inwardly spaced from the inner circumference of said lower ring for defining an annular throat therebetween for upwardly flowing carrier air, valving means movable relative to said extension and operable at a level below said throat for varying the effective flow area of said throat, and means for supporting and actuating said valving means comprising an axially disposed member extending upwardly with in said extension.

4. In a pulverizer comprising a casing having an outlet in its upper portion for pulverized material suspended in carrier air, upper and lower grinding rings in a lower portion of the space enclosed by said casing, a circular series of grinding balls intermediate said rings and cooperating therewith to define a pulverizing zone, means for feeding raw material to said zone adjacent the outer periphery thereof, a stationary support for and below the lower of said .rings for maintaining said lower ring in predetermined axial position, means axially fixed in relation to said lower ring and forming an annular throat of constant available flow area adjacent the inner circumference of .said lower ring for upward flow of carrier air into said zone, valving means independent of and movable relative to said means forming said throat for adjusting the efiective flow area of said throat substantially throughout its circumference, said flow area adjusting means being movable to a position clear of said throat for rendering effective the total available flow area of said throat, means for controlling the movement of said movable means from a location exteriorly of said casing, said last named means comprising operating means extending laterally of and through said stationary support, and stop means for limiting throat area reducing movement of said valving means. 7

5. In a pulverizer comprising a casing having an outlet in its upper portion for pulverized material suspended in air, a circular row of grinding balls in a lower portion of said casing, upper and lower grinding rings cooperating with said grinding balls to define a grinding zone for raw material fed to said zone from the upper side thereof adjacent the outer periphery of said upper ring, a drive shaft coaxial with said rings and said row of balls, power transmitting means connected to said drive shaft for rotating said upper ring relative to said lower ring thereby causing said balls to roll relative to both of said rings, said power transmitting means having a downwardly directed tubular extension axially fixed in relation to said lower ring and flaring outwardly adjacent its bottom edge for defining with the inner circumference of said lower ring an annular throat for carrier air, means for causing an upward flow of carrier air through said throat into and through said grinding zone, and valving means annularly arranged and operable below the entrance to said throat and movable axially of said throat relative to said extension for adjusting the extent of throat area effective for said upward flow of carrier air, said last named means being movable from an upper position adjacent said throat to a lower and more remote position clear of said throat for rendering effective the maximum available flow area of said throat.

6. In a pulverizer comprising a casing having an outlet in its upper portion for pulverized material suspended in carrier air, upper and lower grinding rings coaxially arranged in a lower portion of the space enclosed by said casing, a circular series of grinding balls intermediate said rings and cooperating therewith to define a pulverizing zone, driving means rotatable about the axis of said rings for rotating said upper ring and thereby causing said balls to roll relative to both of said rings, means rotatable with said driving means extending downwardly through said pulverizing zone to form with the inner periphery of one of said rings an annular throat of constant area for upward flow of carrier air into said zone, means forming a circular series of ports for directing carrier air inwardly to a space below said throat, and annularly arranged valving means reciprocable axially of said throat relative to said rotatable means for varying the effective flow area of said throat, said reciprocable means being movable to a position clear of said throat for rendering effective the total flow area available between the opposing walls of said throat, said reciprocable means being formed as a circular band of gradually increasing diameter toward its lower edge to serve as a guide for air flowing from said ports to said throat.

7. In a pulverizer comprising a casing having an outlet in its upper portion for pulverized material suspended in carrier air, upper and lower grinding rings in a lower portion of the space enclosed bysaid casing, a circular series of grinding balls intermediate said rings and cooperating therewith to define a pulverizing zone, m ans axially and radially fixed in relation to the lower of said rings and forming therewith an annular throat-of constant available flow area adjacent the inner circumference of said lower ring for upward flow of carrier air into said zone, and independent adjustable valving means movable transversely of said throat for rendering en'ective different proportions of said available throat area, said valving means comprising a series of circumferentially distributed elements each in slidable engagement with an under surface associated with said lower ring.

8. In .a pulverizer comprising a casing having an outlet in its upper portion for pulverized material suspended in carrier air, upper and lower grinding rings in a lower portion of the space enclosed by said casing, a circular series of grinding balls intermediate said rings and cooperating therewith to define a pulverizing zone, means axially and radially fixedin relation to the lower of said rings and forming therewith an annular throat of constant available area adjacent a marginal circumference of said lower ring for upward flow of carrier air into said zone, and a ring structure arranged coaxially of said throat and formed of segmental portions independently movable transversely thereof for annularly adjusting the effective flow 'area of said throat.

9. In a pulverizer comprising a vertically disposed substantially cylindrical casing having an outlet in its upper portion for pulverized material suspended in carrier air, upper and lower grinding rings in a lower portion of the space enclosed by said casing, a-circular series of grinding balls intermediate said rings and cooperating therewith to define a pulverizing zone, means for rotating one of said rings and thereby causing said balls to roll relative to both of said rings, means rotatable with said rotated ring and extending downwardly through said pulverizing zone to form an annular throat of constant area for upward flow of carrier air into said zone, an annular support adjacent the inner circumference of the lower of said rings for said lower ring below said ring and annularly spaced from said casing, said support having a series of ports therein distributed throughout its circumference for directing carrier air inwardly to a space be low said throat, annular wall means extending from said support to said casing for defining an annular air compartment open throughout its inner circumference to the inlet ends of said ports, inlet means for admitting carrier air to said compartment at a location circumferentially removed from some of said ports a greater distance than from others, and annularly arranged valving means movable relative to said throat for selectively varying the effective flow area dimensions of said throat in different amounts at different circumferential locations.

10. In a pulverizer comprising a casing having an outlet in its upper portion for pulverized material suspended in carrier air, upper and lower grinding rings in a lower portion of the space enclosed by said casing, a circular series of grinding balls intermediate said rings and cooperating therewith to define a pulverizing zone, means forming an annular throat of constant available area adjacent a marginal circumference of said lower ring for upward flow of carrier air into said zone, a segmental ring arranged coaxially of said throat and formed of portions adjustable radially in relation thereto for varying the effective flow area dimensions of said throat substantially throughout its circumference, and means for simultaneously adjusting a plurality of said segmental ring portions.

ll. In an air swept pulverizer adapted for operation over different ranges of output capacities, wherein air is caused to pass through the grinding zone of said pulverizer in quantities proportionate to pulverizer output capacities throughout each range, said pulverizing zone including a series of grinding elements operable in a circle about a central axis to provide a pulverizing zone of generally annular formation, means forming an annular throat of constant available flow area for admitting said air to said zone marginally of said series of grinding elements in an annular stream of maximum cross section for capacities in a high capacity range, and means for admitting said air to said zone in an annular stream of minimum cross section for capacities in a lower capacity range, said last named means comprising annularly arranged valving means independent of and adjustable relative to the opposing walls of said throat for rendering varying proportions of said constant available flow area effective, said adjustable means being movable into an advanced position adjacent said throat for providing said minimum cross section of stream and into a retracted position clear of said throat for providing said stream of maximum cross section.

12. In an air swept pulverizer adapted for operation over successive ranges of output capacities, wherein the quantity rate of air flow through the grinding zone of said pulverizer is increased with increasing capacities throughout each range, means Iorming said grinding zone comprising a ring member having an annular grinding surface together with a circular row of grinding elements rollable in relation to said surface, means arranged concentrically with respect to said ring member and annularly spaced from a periphery thereof to form an annular throat therebetween of fixed available flow area, means for directing carrier air upwardly through said throat from a pulverizer space below said ring member, valving means independent of and adjustable within said space relative to the opposing walls of said throat substantially throughout the circumference of said throat for varying the extent of said throat area effective for difierent ranges, means for adjusting said last named means from a position rendering a minimum amount of said fixed available throat area effective to a position rendering the total amount of said throat area effective, means for maintaining the adjustment of effective flow area constant for any given component range, and stop means for limiting throat area reducing movement of said valving means.

13. In a pulverizer comprising a casing having an outlet in its upper portion for pulverized material suspended in carrier air, upper and lower grinding rings in a lower portion of the space enclosed by said casing, a circular series of grinding balls intermediate said rings and cooperating therewith to define a pulverizing zone, means axially and radially fixed in relation to the lower of said rings and forming therewith an annular throat of constant available area adjacent a marginal circumference of said lower ring for upward flow of carrier air into said zone, and a substantially continuous ring structure arranged coaxially of said throat and formed of portions movable transversely thereof for annularly adjusting the effective flow area of said throat.

GEORGE E. EBERSOLE.

REFERENCES CITED The following referen ces are of record in the file of this patent:

UNITED STATES PATENTS Certificate of Correction Patent No. 2,473,514 June 21, 1949 GEORGE B. EBERSOLE It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 10, lines 60 and 61, strike out adjacent the inner circumference of the lower of said rings and insert the same in line 59, before the word for;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 16th day of May, A. D. 1950.

THOMAS F. MURPHY,

Assistant G'ommiuioner of Patents. 

